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X-CSE-ConnectionGUID: RoOGr5/BSnCBdg/70iNPOQ== X-CSE-MsgGUID: g8IqWIcTQ9Ky/KeVrZTCOA== X-IronPort-AV: E=McAfee;i="6800,10657,11735"; a="74145356" X-IronPort-AV: E=Sophos;i="6.23,130,1770624000"; d="scan'208";a="74145356" Received: from fmviesa009.fm.intel.com ([10.60.135.149]) by fmvoesa113.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Mar 2026 12:42:28 -0700 X-CSE-ConnectionGUID: lu07U/svTcOi6H27MkjM+Q== X-CSE-MsgGUID: kCOGK3keQBSfNRoTO4D0Gg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.23,130,1770624000"; d="scan'208";a="217205494" Received: from dnelso2-mobl.amr.corp.intel.com (HELO [10.125.109.109]) ([10.125.109.109]) by fmviesa009-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Mar 2026 12:42:27 -0700 Message-ID: <554c886f-6678-4208-8566-15aa140f6c4b@intel.com> Date: Fri, 20 Mar 2026 12:42:25 -0700 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 01/22] x86/mm: split out preallocate_sub_pgd() To: Brendan Jackman , Borislav Petkov , Dave Hansen , Peter Zijlstra , Andrew Morton , David Hildenbrand , Vlastimil Babka , Wei Xu , Johannes Weiner , Zi Yan , Lorenzo Stoakes Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, x86@kernel.org, rppt@kernel.org, Sumit Garg , derkling@google.com, reijiw@google.com, Will Deacon , rientjes@google.com, "Kalyazin, Nikita" , patrick.roy@linux.dev, "Itazuri, Takahiro" , Andy Lutomirski , David Kaplan , Thomas Gleixner , Yosry Ahmed References: <20260320-page_alloc-unmapped-v2-0-28bf1bd54f41@google.com> <20260320-page_alloc-unmapped-v2-1-28bf1bd54f41@google.com> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: fxdwdd3i54cf8qn7qj3d8b7iex5u6xwn X-Rspam-User: X-Rspamd-Queue-Id: 73A4A120010 X-Rspamd-Server: rspam12 X-HE-Tag: 1774035749-649444 X-HE-Meta: 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 iBnpyUvb ZNNKTaIc8GFRzSW0ZmyCGFPVi1lUlRDfIKFPcfprgNt3l4uubbxV1OKAdD4w/2nBEIs4+JM7RfOLQym0i4eDcLfLLunWEv5xD7WlhupsEYZ42ocieQNdof+tN8TxyMOXRdhIZ5AszWsoV2Ld2TyEcPYnjlBrqH/3bwSU2zeXm+m8e8aw1McNMJoTxpvUEINgFu9ZCMwposyEaktIrzGMGLbAyTAf4AbuuHzIWceT75Pjil11Yq/X9BLfU5t6lCQzD/vLJ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/20/26 11:23, Brendan Jackman wrote: > - /* > - * The goal here is to allocate all possibly required > - * hardware page tables pointed to by the top hardware > - * level. This comment is pretty important, IMNHO, and you zapped it. The problem here is that the per-MM carved out space is PGD-sized. You want to make sure there are page tables allocated for that space. But, if you say "go allocate a p4d" then that will collapse down to doing nothing on a 4-level system. So, this is effectively: Go allocate a p4d or pud, depending on if it's 4 or 5 level. Basically, always allocate the level that the hardware PGD points to. Could we put a comment to that effect around somewhere, please?